Chemistry 141 Lab

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Chemistry 141 Lab
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Safety Rules

• Do not engage in horseplay in the lab at any
  time. It will not be tolerated for any reason.
• Do not perform any lab work without your
  instructor present. This includes working on
  experiments, using lab glassware, and/or using
  reagents and lab chemicals. You may work on lab
  reports, graphing, or study in the lab without
  the instructors presence.
• In order to make up an experiment you must first
  obtain the approval of your instructor. You must
  then obtain the permission of the instructor in
  whose lab you wish to work. Finally, you must
  inform the stockroom technicians.

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Safety Rules

• You must wear approved eye protection at all
  times when anyone is doing lab work. You must
  wear closed toe shoes (not sandals) to protect
  your feet against broken glass and spilled
  reagents. We recommend that you wear a lab apron
  or old clothing.
• In case of injury, fire, or other mishap, inform
  the instructor at once. If the instructor is not
  in the immediate area inform the chemistry
  technician in the stockroom.

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Safety Rules

• Do not put anything in your mouth while in the
  lab. You are not allowed to eat, drink or smoke
  in the lab.
• Use a fume hood in order to avoid prolonged
  contact with noxious vapors or poisonous gases.
• Immediately use water to rinse off corrosive
  chemicals from your skin or eyes. Notify an
  instructor. Wash your hands before leaving the
  lab for the day. Some chemicals can be readily
  absorbed through the skin.

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Safety Rules

• Use a lubricant such as glycerine to insert glass
  tubing or a thermometer into a rubber stopper.
  Hold the piece of glass which is being inserted
  or removed close to the end with a paper towel.
• Clean up spills and breakage immediately.
  Neutralize acids or base spills with sodium
  bicarbonate before washing down the area with
  water.

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Safety Rules

• Familiarize yourself with the safety equipment in
  the lab, including the first aid kit, fire
  blanket, fire extinguisher, the safety shower,
  and the eye wash station.
• When heating the contents of a test tube, point
  the open end of the tube away from everyone. A
  vapor pocket may form beneath the surface of the
  contents and cause their ejection (bumping).

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Safety Rules

• Dispose of insoluble waste in the waste basket,
  not in the sink. Broken glass is to be disposed
  in the broken glass receptacle.
• Be sure to read the labels on all chemical
  reagent containers before using their contents.
  Using an improper reagent for an experiment can
  lead to a serious accident.

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Safety Rules

• Do not take chemical reagent containers to your
  work bench. Leave them at their initial
  location. Do not use any of your lab equipment
  to dispense chemicals for an experiment. The
  instructor will demonstrate the proper method for
  dispensing chemicals.
• Chemicals are expensive items therefore, transfer
  out only what you will need for the experiment.
  Do not ever return used or excess chemicals to
  their original containers to prevent
  contamination.

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Safety Rules

• At the conclusion of your lab period thoroughly
  clean up your work area. Make sure that the gas
  to the bunsen burner is shut off. Do not remove
  any chemicals or lab equipment from the
  laboratory.

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Lab Books

• Get a lab book with prenumbered carbonless copy
  pages. Write your name on the front of the lab
  book.
• All data in the lab book must be written in ink.
• Do not tear any original pages out of the book!!

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Lab Books

• Begin each lab with a title
• Enter the date you are beginning the experiment,
  your name, and list any lab partners you may be
  working with.
• Everyone will do the entire lab on their own, but
  you may want to work with someone else to compare
  your results

• August 20, 2007
• Luna Lovegood
• Experiment 1 Standard Deviation Lab
• Worked with Hermione Granger

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Lab Books

• Reference the procedure and note any safety
  precautions.

• Procedure Followed procedure outlined in the lab
  manual.
• Lehman, J. Olmstead, T. et al (2002). 
  Experiment 2 Measuring Density using different
  types of Glassware.  In Grossmont College
  Chemistry 141 Laboratory Manual (4th Edition, pp.
  5-10). El Cajon, California.
•  Safety Wear Safety glasses

Or if you used the Online Lab Manual Lehman, J.,
Olmstead, T.  et al (2002).  Experiment 2
Measuring Density using different types of
Glassware Electronic version.  Grossmont
College Chemistry 141 Laboratory Manual, 5-10.
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Lab Books

• Data and Observations
• This should be a log of what you saw along with
  any tables of data that may be necessary

Trial Mass beaker water Mass beaker after pouring water out Mass Water delivered by beaker
1
2
3
I filled the beaker to the 50 mL line with an
eyedropper. It was very difficult to determine
when the water level reached the line on the
beaker.
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Lab Books

• Be sure to write all data in your lab book in
  black or blue ink when you take the data. The
  only exception will be for data collected by the
  computer. Any data recorded on stray pieces of
  paper will be confiscated!

• No writeovers
• 375.788g
• No obliterations
• 639.824g
• No Erasing
• Cross out once and rewrite.
• 4.932g
• 5.382g

636
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Lab Books

• At the end of the lab period, sign and date your
  lab book after your last data entry and get an
  instructor stamp.

• Copper sulfide precipitate was filtered and left
  in lab drawer to dry. The precipitate was a very
  fine black powder.
• Luna Lovegood
• 9/28/07
• Severus Snape
• Potions Instructor

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Lab Reports

• Typewritten reports documenting your experimental
  results. Some reports will be abbreviated as
  noted in write-up instructions.
• Be sure to clearly label each section!

• Title Page
• Objective
• Introduction
• Procedure
• Results and Calculations
• Discussion
• Conclusion
• Questions

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Title Page

• Standard Deviation Experiment
• Luna Lovegood
• Chemistry 141
• S. Snape
• Section 5399
• September 3, 2007

• This will identify you, your class, and the
  experiment. Very important so I can keep track
  of what you are handing in!
• Be sure to include the grading rubric.

Lab Notebook Lab Notebook Lab Notebook /25
Procedure Procedure /5
Signatures Signatures /5
Data Data /15
Formal Report Formal Report Formal Report /75
Title Page /5
Objective /10
Introduction /15
Procedure /5
Results and Calculations /15
Discussion /15
Conclusion /10
Total Total Total /100
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Objective

• Why are you doing this experiment?

• Objective
• To determine the accuracy and precision of
  laboratory glassware and to learn how a standard
  deviation is calculated. To determine the
  density of some unknown liquids.

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Introduction

• This section tells a little bit about the theory
  of the experiment and how it will be done.

• Introduction
• When doing scientific experiments it is always
  necessary to minimize the error where possible.
  Unfortunately, however, it is impossible to
  completely avoid error. In experiments there are
  several types of error. They are random error,
  systematic error, and gross error. Random error
  is---

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Procedure

• Reference the procedure used and note any
  deviations from the published procedure.

• Procedure
• Followed procedure from lab book
• Lehman, J. Olmstead, T. et al (2002). 
  Experiment 2 Measuring Density using different
  types of Glassware.  In Grossmont College
  Chemistry 141 Laboratory Manual (4th Edition, pp.
  5-10). El Cajon, California.
• In this experiment the liquids used for the
  density determinations were an water, coke, and
  diet coke.

Or if you used the Online Lab Manual Lehman, J.,
Olmstead, T.  et al (2002).  Experiment 2
Measuring Density using different types of
Glassware Electronic version.  Grossmont
College Chemistry 141 Laboratory Manual, 5-10.
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Results and Calculations

• Tabulate data and any calculated values. Show
  sample calculations. (These may be hand
  written.)
• For non numerical labs, summarize the data
  generated.

Results and Calculations
Trial Mass beaker liquid (g) Mass beaker after dispensing liquid(g) Mass liquid(g) Average mass liquid deviation Standard deviation
1 xx.x xx.x xx.x xx. .xx .xx
2 xx.x xx. xx.x xx.x .xx .xx
3 xx.x xx.x xx.x xx. x.x .xx
Sample Calculation for mass liquid xxx.xxg-xx.xxg
xx.xxg
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Discussion

• This is where you get to explain your results

• Discussion
• The average mass of water held by the beaker was
  43.2g. This was less than expected based on the
  marking on the beaker. The mass of water held
  was probably low because I filled my beaker to
  the bottom of the line and it may have been
  designed to fill to the top of the line. I also
  noticed that---

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Conclusion

• Conclusion
• The beaker held 53.4 grams of water with a
  standard deviation of 0.7 g. The graduated
  cylinder held 10.2 grams of water with a standard
  deviation of 0.1 g. The densities of regular
  Coke and diet Coke were

• This is where you give the final result. This is
  essentially the punch line--

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Questions

• Answer any questions posed in the lab here.

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Precision and Accuracy

• Accuracy -- Refers to how close to the true value
  a given measurement is.
• Precision -- Refers to how well a number of
  independent measurements agree with one another.

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Error Analysis

• Types of error
• Random
• Systematic
• Gross

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Error Analysis

• Types of error
• Random
• Not mistakes but inherent in measuring process.
• May be positive or negative.
• Cause the data to be spread symmetrically around
  the true value
• May be minimized by doing repeated trials of an
  experiment
• Systematic
• Gross

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Error Analysis

• Types of error
• Random
• Systematic
• Caused by consistently making the same mistake
  for all measurements.
• Tend to give precise though incorrect results.
• May be minimized by using different techniques to
  gather data.
• Gross

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Error Analysis

• Types of error
• Random
• Systematic
• Gross
• Results in a value which is far different than
  either the true value or the mean
• Caused by sample inconsistencies or experimental
  error (ie reading measuring instrument wrong on
  one trial)

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Definitions

• Mean value the average
• Median value Middle value
• Spread or range difference between highest and
  lowest measurement
• Deviation difference between mean and any
  specific measurement

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Average Deviation
Trial Mass
1 9.6
2 9.8
3 10.3
4 10.0
5 10.8
6 9.5
Mean 10.0
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Average Deviation
Trial Mass Deviation
1 9.6 -0.4
2 9.8 -0.2
3 10.3 0.3
4 10.0 0.0
5 10.8 0.8
6 9.5 -0.5
Mean 10.0 0.0
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Average Deviation
Trial Mass Deviation /dev/
1 9.6 -0.4 0.4
2 9.8 -0.2 0.2
3 10.3 0.3 0.3
4 10.0 0.0 0.0
5 10.8 0.8 0.8
6 9.5 -0.5 0.5
Mean 10.0 0.0 0.4
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Standard Deviation

• s represents the standard deviation
• d represents the individual deviation
• n is the number of trials.

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Standard Deviation
Trial Mass Deviation /dev/ (dev)2
1 9.6 -0.4 0.4 .16
2 9.8 -0.2 0.2 .04
3 10.3 0.3 0.3 .09
4 10.0 0.0 0.0 .00
5 10.8 0.8 0.8 .64
6 9.5 -0.5 0.5 .25
Mean 10.0 0.0 0.4 Sum1.57
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Standard Deviation
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Standard Deviation
s 0.6 g So 68 of measurements lie between 9.4
and 10.6 grams 95 of measurements lie between
8.8 and 11.2 grams gt99 of measurements lie
between 8.2 and 11.8 grams
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Significant Figures

• Significant digits -- refers to the total number
  of digits in a measurement where one of the
  digits is uncertain and the others are certain.
• According to standard deviation calculations, the
  last digit is uncertainsig figs work pretty well
  in the absence of statistical work-up!

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Rules for determining number of significant
figures

• All non-zero digits are significant.
• All zeros between nonzero digits (or significant
  zeros) are significant.
• Zeros used as placeholders are not significant.
• all zeros to left of 1st non-zero digit are not
  significant. (For example 0.0068 -- two sig figs
  the zeros are placeholders.)
• for numbers greater than 1, zeros to the right of
  last digit are ambiguous if no zeros after
  decimal point. Assume not significant for this
  class.
• Zeros after last digit are significant for
  numbers lt1 or if they occur after decimal point
  for number gt1.
• Exact numbers have an infinite number of
  significant figures.

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Calculations with Significant Figures

• In addition and subtraction, the last digit
  retained in the sum or difference is determined
  by the position of the first doubtful digit.
• For example 37.24 1002.46
• 10.3 6.3
• ------------- ---------------
• 47.54 1008.76
• Rounds to 47.5
  1008.8

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Calculations with Significant Figures

• In multiplication and division, an answer has no
  more sig figs than the measurement with the least
  number of sig figs.
• For example 3.427 x 0.00692 0.02371484 0.0237

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Experiment

• You will measure the mass of water delivered by a
  beaker and by a graduated cylinder multiple times
  and determine the mass of water delivered with
  each instrument and the standard deviation. You
  will then determine the density of regular and
  diet Coke using the most appropriate tools.
• Results will be entered on the spreadsheet at
  www.grossmont.edu/cwillard.

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Sample Data Table
Temperature of water_______________ Density of
water at measured temperature_________ Balance
used ______________________
Trial number Mass beaker 50 ml water (g) Mass drained beaker (g) Mass water (g) Volume water (mL) (calculated from density) Deviation Deviation2
1
2
3
Sum
Mean